Goosebumps Measurement
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Goosebumps measurement Psychophysiology and measures of pilo-erection in humans SWISS CENTER FOR AFFECTIVE SCIENCES September 30, 2016 Authored by: Dr. Sylvain Delplanque Goosebumps measurement Psychophysiology and measures of pilo-erection in humans Report outline This report synthesizes the current knowledge about the piloerection phenomenon in humans and the different methodologies developed to measure it. After a short introduction to the physiology of piloerection, different lines of measurement development are proposed. This report is written with one objective in mind: to provide the reader the key knowledge on piloerection that would provide a starting point to develop a reliable method for its measurement. We thus propose to incrementally enrich this report as a function of the questioning and discussions between the two parties. This strategy should allow a flexible and efficient way to focus the knowledge on the important points. The relevant existing literature is also provided (via separate files) to allow the reader to further explore the topic if needed. Key concepts - Goosebumps correspond to epidermis buckles created by contraction of multiunit smooth muscles arrector pili attached to the skin hair - Piloerection is involved in themoregulation, emotional reactions and particular pathological states. Induction via individually adapted pieces of music is the most reliable way to induce goosebumps. - Piloerecdtion have been reported to be maximal over forearms - Piloerection is triggered by the sympathetic branch of the autonomic nervous system (α1-adrenergic receptors) - Arrector pili contractions are graded and slow - Goosebumps are already measured via detection of spatial frequency changes in the visual domain or mechanical distortion of the skin via deformation of spiral coplanar capacitors - To date, the electromyographical response of arrector pili muscles during piloerection is not characterized - The main challenge will be to isolate the specific response from the background noise (large movements, electrical activity of underlying skeletal muscles) - Spatiotemporal decomposition of the electromyographical signal seems to be a key strategy to isolate piloerection signal from surrounding noise - High density arrays of Ag/AgCl contact electrodes could be used in a first phase to maximize the likelihood of observing the signal KEYWORDS for literature research: goose pimples OR goose flesh OR goose bumps OR shivering 9/30/2016 | Introduction to Goosebumps For most mammals, piloerection (causing goose bumps, flesh or pimple) is a common method of modifying heat exchange. It is caused by the contraction of the arrecto pili muscles (AP), which are bodies of smooth muscle that extend from the fibrils of the dermis into connective tissue investment of the hair follicle. In many species, including familiar ones such as dogs, cats, and chimpanzees, raising the hair serves a secondary function of social warning of impending aggression. As humans possess relatively little hair and are often clothed, heat conservation through piloerection is usually regarded as insignificant and rudimentary. However, piloerection may become more important Goosebumps measurement 1 in conjunction with shivering, potentially enhancing the effectiveness of the shivering response. In human, piloerection is most often known as a reaction to cold and also to strong emotional stimuli. Goosebumps are caused by arrector pili muscles contractions The arrector pili muscle is a small band of smooth muscle that connects the hair follicle to the connective tissue of the basement membrane in non glaborous skin. In response to increased sympathetic nerve discharge, the arrector pili muscles at the base of tiny hairs in the skin contract and cause the hairs to become upright, trapping air and thus increasing the insulating layer of air around the body and minimizing heat loss. This is known as piloerection. As the muscle contracts, the epidermis buckles, creating “goosebumps” that are easily visible (Figure 1) and strongly elicited in forearms. The density of goosebumps at this location is around 16-18 hair follicles per cm2 (Benedeck et al., 2010; Otberg et al., 2004) and a single goosebumps radius has been reported as around 2 mm (Kim et al., 2014). Note: it seems more plausible that this value corresponds to the diameter. FIGURE 1GOOSEBUMPS IN HUMANS Each hair follicle was once believed to be attached to a separate APM, but this has been refuted by more recent studies. Poblet et al. proposed that the APM associated with follicles in one follicular unit converge into one muscular unit and hence that all follicles within a unit share a single muscle. In a study conducted by Song et al., the structure of the APM was evaluated by three-dimensional reconstructions. The authors reported a variation in which two follicular units can share a single APM. They also suggested that only one muscular structure is involved in the follicular unit, which inserts tightly to the furthest follicle. Song et al. also reported that the APM forms a concave support for the sebaceous gland lobules. These lobules are located between the follicles and APM, forming an angular area. 9/30/2016 | Goosebumps measurement 2 FIGURE 2 CROSS-SECTION OF ALL SKIN LAYERS Arrector pili muscles are multiunit smooth muscles Smooth muscles are composed of small, tapered cells with single nuclei, Smooth muscle cells do not have T tubules and have only loosely organized sarcoplasmic reticula. The calcium required for contraction comes from outside the cell and binds to a protein called calmodulin, rather than to troponin (as for skeletal muscles) to trigger a contraction event. The lack of striations in smooth muscles fibers results from the fact that the thick and thin myofilaments are arranged quite differently than in skeletal of cardiac muscles fibers. Because the myofilaments are not organized into sarcomeres, they have more freedom of movements and as a result can contract a smooth muscle fiber to shorter lengths than in skeletal and cardiac muscle. 9/30/2016 | Goosebumps measurement 3 FIGURE 3 A SERIES OF AXON-LIKE SWELLING, CALLED VARICOSITIES OR “BOUTONS,” FROM AUTONOMIC NEURONS FORM MOTOR UNITS THROUGH THE SMOOTH MUSCLE Artrector pili muscles are multiunit smooth muscles, meaning that they do not act as a single unit (as single-unit visceral muscles) but instead is composed of many independent single-cell units. Each independent fiber does not usually generate its own impulse but rather responds only to nervous input (i.e., neurogenic activation). This type of smooth muscles are often found in bundles like in the case of the APM. The main consequence of APM physiological properties is that its contraction is graded, meaning that it is theoretically plausible to measure variations in contraction intensity. Of particular importance are the high metabolic economy of smooth muscle, which allows it to remain contracted for long periods with little energy consumption, and the small size of its cells, which allows precise control of very small structures, such as blood vessels. The contraction of smooth muscle is much slower than that of skeletal or cardiac muscle, it can maintain contraction far longer and relaxes much more slowly. The source of these differences lies in the chemistry of the interaction between the different proteins that composed smooth muscles fibers. Piloerection can be evoked centrally and peripherally APM are present throughout hairy skin and are activated centrally by cold exposure, fever, and strong emotions. In the periphery, piloerection is evoked directly by mechanical, thermal, electrical, or pharmacological stimuli or, as previously reported, indirectly via an axon reflex. Piloerection is generally not under voluntary control. It is used as an index of autonomic sympathetic activity and is thought to be mediated by α1-adrenergic receptors. Piloerection, sebaceous and sweat secretions 9/30/2016 | Goosebumps measurement 4 FIGURE 4: SEBACEOUS, ECCRINE AND APOCRINE GLANDS IN RELATION TO FOLLICLE HAIR The skin of most mammals is characterized by the presence of sebaceous glands (see Figure 4), which produce lipid- containing sebum. Sebum contributes to the large majority of skin surface lipids, which are crucial for hair growth, moisturization of skin and hair, and the prevention of water evaporation from the skin surface. Recent research has suggested that sebum may also contain antioxidants, antimicrobial lipids, and pheromones. In humans, sebum excreted by the sebaceous glands is primarily composed of triacylglycerides, wax esters, and squalene (Zhang et al., 2014). To date, there is no reported evidence of a direct relationship between goosebumps elicitation and sebaceous secretions. Sweat is emitted via two types of glands: apocrine and eccrine glands. Apocrine glands are anatomically linked to the hair follicle (Figure 4), the sweat being secreted in the pilary canal of the hair follicle. Apocrine sweat glands are found in the armpit, around the nipples, between the anus and genitals, in the ear, and in the eyelids. They become active after the puberty, contain complex chemical compounds (sometimes related to pheromone-like effects) whose degradation by the skin bacteria produce the sweat odour. With regards to their distribution, the relation between piloerection and apocrine glands is unlikely to be functionally informative. Eccrine glands are more broadly distributed and can be found at places where piloerection has been reliably measured (foreharm).